Induction of tumor-specific immunity is an attractive approach for cancer therapy because of the prospect of harnessing the body's own defense mechanisms, rather than using standard toxic therapeutic agents, to provide long-term protection against tumor existence, growth and recurrence. This strategy is attractive for its potential to destroy small metastatic tumors which may escape detection, and to provide immunity against recurrent tumors.
In principle, an immunotherapy would depend on the presence of tumor-specific antigens and on the ability to induce a cytotoxic immune response that recognizes tumor cells which present antigens. Cytotoxic T lymphocytes (CTL) recognize major histocompatibility complex (MHC) class I molecules complexed to peptides derived from cellular proteins presented on the cell surface, in combination with co-stimulatory molecules. Mueller et al., Annu. Rev. Immunol. 7: 445-80 (1989). In fact, tumor-specific antigens have been detected in a range of human tumors. Roth et al., Adv. Immunol. 57: 281-351 (1994); Boon et al., Annu. Rev. Immunol. 12: 337-65 (1994).
Some cancer vaccination strategies have focused on the use of killed tumor cells or lysates delivered in combination with adjuvants or cytokines. More recently, gene transfer of cytokines, MHC molecules, co-stimulatory molecules, or tumor antigens to tumor cells has been used to enhance the tumor cell's visibility to immune effector cells. Dranoff & Mulligan, Adv. Immunol. 58: 417-54 (1995).
The therapeutic use of “cancer vaccines” has presented major difficulties, however. In particular, conventional approaches require obtaining and culturing a patient's autologous tumor cells for manipulation in vitro, irradiation and subsequent vaccination, or the identification and purification of a specific tumor antigen.